1. Field of the Invention
The present invention relates to a rewritable image display medium and a manufacturing method thereof.
2. Description of the Related Art
As repeatedly rewritable image display devices, image display devices for displaying an image using particles moved by an electric field are known. Such image display devices include an image display medium where electrically conductive colored particles and insulating white particles are sealed between a transparent display board and a back board facing the display board with a minute gap.
The image display medium applies an electric field between the display board and the back board and injects electric charges into the electrically conductive colored particles so as to move the colored particles towards the display board side by means of the action of the electric field and display an image according to contrast between the colored particles and the white particles.
In order to display a uniform and stable image in such an image display medium, therefore, it is important to maintain a uniform gap between the display board and the back board and evenly distribute the colored particles on the display surface. For this reason, in a conventional technique a spacing member is formed between the display board and the back board, so that the constant gap is maintained and the gap between the boards is partitioned into a plurality of cells (see Japanese Patent Application Laid-Open (JP-A) No. 2001-33833).
As shown in FIG. 9, however, when a spacing member 106 is formed on a back board 104, for example, a gap is generated between a display board 102 and the spacing member 106 due to variance in the height of the spacing member 106. Further, when an image display medium 100 is manufactured, colored particles 108 are occasionally caught between the spacing member 106 and the display board 102, and thus a gap is generated between the display board 102 and the spacing member 106.
In the case where the gap is generated between the spacing member 106 and the display board 102, as an image is repeatedly displayed, the colored particles 108 move gradually between the cells through the gap, and a quantity of the colored particles varies among the cells. Mosaic-like irregularity of display density and defective dots occur due to the movement of the colored particles 108 between the cells, and thus a stable image is not displayed.